Process for suspension polymerization

ABSTRACT

A process for suspension polymerization of vinyl monomers in an aqueous liquid medium wherein an inorganic compound difficultly soluble in the liquid medium and a resinous substance, having a solubility parameter value of from 7.8 to 16.1 and being soluble in the vinyl monomers are kneaded in advance with the vinyl monomers, and the kneaded mixture is then suspended in the liquid medium to polymerize the vinyl monomers.

United States Patent 91 Ohe et al.

[ Feb. 13, 1973 I PROCESS FOR SUSPENSION POLYMERIZATION [75] lnventors:Keltaro Ohe; Daijiro Nishio; Shigeru Sadamtsu; Hiroyuki Kaneko, all ofKanagawa, Japan [73] Assignee: Fuji Photo Film Co.,

Kanagawa, Japan [22] Filed: May 22, 1970 [21] Appl. No.: 40,482

Ltd.,

[30] Foreign Application Priority Data May 23, 1969 Japan ..44/40057[52] US. Cl. ..260/17 A, 260/l7 R, 260/341, 260/40 TN, 260/41 A, 260/41B, 260/41 R,

[51] int. Cl. ..C08f l/ll [58] Field of Search ..260/l7 A, 17 R, 41 A,41 B, 260/41 R, 95, 34.2, 703,878; 241/30 [56] References Cited UNITEDSTATES PATENTS 3,198,775 8/1965 Delacretaz et a1. ..260/17 R 3,205,2049/ 1965 Heckmaier et a1 ..260/17 R 3,222,343 12/ 1965 Ingram et a1..260/ I 7 R 3,458,603 7/1969 Gritfin ..260/17 R 2,171,765 12/1935 Rohmet a1. ..260/41 C 2,588,398 3/1952 Mast et a1. ..260/86.] R

Primary Examiner-William H. Short Assistant Examiner-L. M. PhynesAttorney-Sughrue, Rothwell, Mion, Zinn and Macpeak 5 7 ABSTRACT 8Claims, No Drawings PROCESS FOR SUSPENSION POLYMERIZATION BACKGROUND OFTHE INVENTION l. Field of the Invention This invention relates to aprocess for suspension polymerization, and particularly to a process forproducing a polymer in the form of finely divided uniform granules orbeads.

2. Description of the Prior Art It has generally been the practice insuspension polymerization to add various dispersing agents to apolymerization system to prevent the resulting polymer from beingagglomerated into a mass. The dispersing agents used for this purposebroadly include watersoluble high-molecular-weight compounds anddifficultly soluble finely divided inorganic compounds. Of thesedispersing agents, the water-soluble high-molecular-weight polymers needto be added only in relatively small amounts and therefore areeconomically advantageous. But they are adsorbed onto the surface of theresulting polymer particles or grafted to the polymer, thereby theremoval of these agents becomes difficult. On the other hand, thesparingly soluble inorganic compounds can be removed relatively easilyby dissolving them in an acid or base. However, they need to be used inconsiderably large amounts for dispersing purposes. Furthermore, the useof the inorganic compounds alone, as described in Japanese PatentPublication No. 537/62, makes it difficult to perform the polymerizationstably, resulting in nonuniform spherical polymer particles withirregular sizes. To avoid this, attempts have been made to addstabilizing agents such as surface active agents. These agents, however,are difficult to remove completely from the. resulting polymers as isthe situation with the water-soluble polymers above.

In any case, according to the processes previously reported, polymerparticles obtained usually have an average diameter of 50 microns ormore, and 30 microns at the smallest, and it is practically impossibleto. produce uniform, spherical fine polymer beads having an averagediameter of about microns or less stable products.

Our research work conducted in an attempt to produce fine particles ofpolymer led to the discovery that when a water-insoluble but relativelyhydrophilic inorganic compound is forcibly kneaded into a monomericvinyl compound which is relatively hydrophobic and the kneaded mixtureis added then to an aqueous medium, the particles of the inorganiccompound migrate to the interface between water and the dispersed phaseof the vinyl mono'm'er and exhibit an effective dispersing action.Consequently this procedure results in fine and uniform particles ofpolymer using small amounts of these inorganic compounds as comparedwith the prior processes in which difficultly soluble inorganiccompounds are added directly to an aqueous medium. This discovery isdescribed in patent application Ser. No. 703,878, filed on Feb. 8, 1968,now abandoned. Further reduction in size of polymer beads couldbe-effected by increasing the amounts of finely divided difficultlysoluble inorganic compounds added to the vinyl monomer. But if amonomeric vinyl compound is mixed with fine powders of the difficultlysoluble inorganic compound of an amount exceeding a certain limit, themixture becomes thixotropic, and it becomes difficult to knead anddisperse the inorganic compounds or to withdraw them from a kneader.

We have therefore made extensive studies to overcome these difficultiesof conventional processes and produce polymers in the form of fine anduniform granules.

Accordingly, an object of the present invention is to provide a processfor producing fine and uniform granular polymers.

SUMMARY OF THE INVENTION The process of this invention comprisessubjecting a monomeric composition comprising at least one vinyl monomerto suspension polymerization in an aqueous medium, characterized in thatan inorganic compound which is difficultly soluble in such liquid mediumand a resinous substance which has a solubility parameter value (SP), asdefined hereinbelow, within the range of from 7.8 to 16.1 and is solublein said monomeric composition are kneaded with said monomericcomposition, the kneaded mixture is then suspended in said liquidmedium, and the vinyl monomer is polymerized in this state.

DETAILED DESCRIPTION OF THE INVENTION In the present invention, aresinous substance (hereinafter called a fluidizing agent) is added inadvance to a suspension polymerization system of the type disclosed inthe patent application mentioned above, thereby remarkably reducing thethixotropy or apparent viscosity of the kneaded mixture and improvingthe kneaded and dispersed state of the mixture. Thus, the kneading anddispersing operations are rendered commercially feasible and easy sothat the desired fine and uniform polymer particles can be producedstably. According to the present invention, a fluidizing agent solublein a polymerizable vinyl monomer is added to said monomer in an amountof from 0.001 to 10 percent by weight based on said monomer, togetherwith a relatively hydrophilic and difficultly soluble inorganic compoundand a polymerization initiator. They are kneaded for a certain period oftime in a ball mill, for example. The kneaded mixture withdrawn from theball mill is suspended in an aqueous medium, and polymerized.

The fluidizing agent used. in the present invention is present dissolvedin the resulting polymer particles. But it has the marked advantage thatsufficient results are obtained with amounts as small as l percent orless, and unlike surfactants, the various surface properties, especiallyelectrical characteristics, of the polymer particles upon adsorptionthereto, are not adversely affected.

The fluidizing agent, which is the most characteristic component inthepresent invention, isa resinous substance having a relatively largepolarity which has a solubility parameter value (abbreviated SP; seePolymer Handbook, Vol. 4, pages 34l-368, John Wiley and Sons (1966)),within the range of from 7.8 to 16.1 and is soluble in the vinylmonomers used. The effective amounts of the fluidizing agent are withinthe range of from about 0.001 to 10 percent by weight based on themonomer. In commercial-scale operations, however, very small amountswithin this range can be used with satisfactory results, and this is anadmined according to the combination of the types and amounts of thevinyl monomer, difficultlysoluble inorganic compound or other additives.

The above-described fluidizing agent is selected from.

natural or synthetic resinous substances having a solubility parameterwithin the range of from 7.8 to 16.1. The SP value is the square root ofthe cohesive energy density, which is a measure of the intermolecularforce, and whether it is large or small corresponds to the polarity ofthe respective substance. Physically, the cohesive energy density is theamount of energy required to evaporate one cubic centimeter of theliquid (solvent). The SP of the resinous substance used as thefluidizing agent of the present invention is calculated from variousphysical constants or determined experimentally. Since the former methodis effective only on those substances whose composition or structure isknown, the latter method is used in most cases in determining the SP.Among the experimental methods are those in which the calculation ismade on the basis of solubilities or degrees of swelling. The methodconsidered to be most effective for commercially available resinoussubstances involves dissolving the resinous substance, intended for useas a fluidizing agent, in many solvents having different SP values,measuring the intrinsic viscosity of the resinous substance in eachsolvent, and adopting the SP of a solvent which gives the maximumintrinsic viscosity as the SP of the fluidizing agent. In thepresent'invention, the following 22 solvents are used to measure theintrinsic viscosities of fluidizing agents at 25C, and the SP ofasolvent which gives the maximum intrinsic viscosity is defined as the SPof the fluidizing agent.

Solvents Solubility Parameter 1. Diisopropyl Ether 6.9 2. n-Hexane 7.33. Diisobutyl Ketone 7.8 4. Cyclohexane 8.2 5. n-Butyl Acetate 8.5 6.Xylol v 8.8 7. Methyl Ethyl Ketone 9.3 8. Methylene Chloride 9.7 9.Acetone 9.9 10. Ethylene glycol monoethyl ether 10.5 1 l. Pyridine 10.712. Nitroethane 11.1 13. n-Butanol 11.4 14. Acetonitrile 1 1.9 15.N,N-Dimethyl Formamide 12.1 16. Ethanol 12.7 17. Nitromethane 12.7 18.Propiolactone 13.3 19. Methanol 14.5 20. Methyl Formamide 16.1 21.Formamide 19.2 22. Water 23.4

The SP of the substance corresponds to the polarity of the substance. Asthe fluidizing agent suitable for the present invention, relativelypolar resinous substances having an SP within the range of from 7.8 to16.1 are suitable. Examples of such are a cellulose ether resin (havingan SP of about 11.4), a polyurethane resin (having an SP of about 10.0),an amino resin (having an SP of about 10.7), an epoxy resin (having anSP of about 13.0), and an alkyd resin (having an SP of about 8.6).

Other components used in the process of the invention are describedhereinafter. The monomeric composition of the invention comprises atleast one vinyl monomer. Such a vinyl monomer is the starting materialfor the polymer desired, and specifically includes, for example,styrene, acrylates, methacrylates, vinyl acetate, vinyl chloride,acrylonitrile, and butadiene. When only one vinyl monomer is used, ahomopolymer results, and when two or more vinyl monomers are used,copolymers result. The solubilities of these vinyl compounds in waterare not more than several percent, and 10 percent at the highest.

The medium in which the suspension polymerization of these vinylcompounds is carried out is an aqueous liquid medium, such as water or amixture of water and a water-soluble liquid. The solubilities of thevinyl compounds in the mixed medium are the same as the solubilities inwater.

The inorganic compounds difficultly soluble in the aqueous liquid mediumpreferably have a high hydrophilicity. These compounds specificallyinclude, for example, metal powders, carbonates, phosphates, halides,oxides, sulfides, sulfates or hydroxides of Mg, Ca, Zn Fe, Co, Ni, A1,Si, Ti, Mn, Cd, Ag, Hg, or Ba, for example, MgCO MgHPO CaCO MnCO CaSOBaSO MgO, TiO,, FeO, Fe O ZnO, A1 0 CuO, SiO PbO,

CuS, AgS, CdS, HgS, AgCl, HgCl PbCl Ca(Ol-l) A1 (Ol-1) or Fe(Ol-l) Theseinorganic compounds have a solubility in water of not more than 10percent and are capable of being present as particles in an aqueousmedium. The average size of these particles is less than several.microns, preferably less than 1 micron. These inorganic compounds areused in amounts of from 10 to 300 percent by weight based on the weightof the vinyl monomer.

As in the conventional processes, the above-mentioned kneaded system, ifdesired, can contain molecular weight regulating agents, lightresistance improving agents, discoloration inhibitors, processabilityimproving agents, coloring pigments, or dyestuffs.

The inorganic compound is present in the as-obtained polymer ina mannerso as to cover the surfaces of the polymer beads. If desired, theinorganic compound can be removed by treatment with a suitable acid orbase, or by washing with water and then drying. Thus, there can beobtained fine and uniform polymer beads.

The invention will now be illustrated by the following working exampleswhich are intended to be exemplary and not limitative.

EXAMPLE 1 Each of the compositions shown in Table l was kneaded in aball mill.

TABLE 1 The kneaded liquid was withdrawn from the ball mill. SamplesNos. 1 and 3 were difficult to remove from the mill because of the lackof flowability in the absence of a fluidizing agent. Sample No. 1 couldnot be withdrawn completely from the mill. Furthermore, agglomeratedparticles of the zinc oxide were observed, and they readily separatedfrom the monomer. On the other hand, Samples Nos. 2 and 4 whichcontained the fluidizing agent were sufficiently flowable, and could bewithdrawn easily from the mill. The zinc oxide particles were welldispersed with hardly any formation of agglomerated particles, and theliquid was stable.

Each of Samples Nos. 2, 3 and 4 was put into a polymerization vesselprovided with a high speed stirrer to which 500 parts by weight ofwater'had been added in advance, while operating the stirrer. Themixture was heated to 90C, and polymerized for 5 hours, followed bycooling. The zinc oxide was dissolved by the addition of 600 parts (forSample No. 2) of hydrochloric acid and 200 parts (for Sample Nos. 3 and4) of hydrochloric acid. The polymerization product was washed withwater and the water removed by means of a centrifugal separator, andthen dried using a flush drier. Very fine and uniformly sphericalpolymer beads were obtained. The withdrawn state of the kneaded mixturefrom the ball mill and the diameters of the obtained polymer particlesare shown in Table 2.

As can be seen from the results obtained that the effect of thefluidizing agent was very remarkable.

EXAMPLE 2 Each of the compositions shown in Table 3 was kneaded in aball mill.

- TABLE 3 (Parts by weight) Sample No. 5 6 Vinyl Monomer MethylMethacrylate l00 I00 Plasticizer Dibutyl Phthalate 20 20 PolymerizationInitiator Benzoyl Peroxide 2 2 Dispersing Agent Basic MagnesiumCarbonate Fluidizing Agent UVAN 32 t 0.2 Butylated urea melamine resinmanufactured by Toyo Koatsu Industry, Inc. (The intrinsic viscosity ofUVAN 32 in a solvent is, for instance, 0.057 in acetone having an SF of9.9. 0.078 in pyridine'having an SP of l0.7, 0.076 in n-butanol havingan SP of ll.4, and 0.060 in ethanol having an SP of 12.7. From theseviscosity values, the SP of UVAN 32 was found to be 10.7.)

Withdrawal of the kneaded mixture of Sample No. 5 was difficult becauseof insufficient flowability, and the magnesium carbonate was prone toseparate from the monomer. In contrast, the kneaded Sample No. 6 wassufficiently flowable, and could be readily removed from the ball mill.Also, the liquid was in a stable condition. Each of these samples waspolymerized in the same manner as in Example 1 to form fine sphericalparticles of the polymer. The withdrawn state of the kneaded mixturefrom the ball mill and the diameters of the obtained polymer particlesare shown in Table 4.

TABLE 4 Sample No. 5 6 Withdrawn State of the Kneaded Mixture from theBall Mill Flowability and Withdrawability bad good Viscosity (CP) 40000350 Grind Gauge (particles) (mil) 4.0 0 Polymer Particle DiameterAverage Diameter (microns) 35 l 1 Particle Diameter Distribution(microns) 5-100 2-1 5 As can be seen from the results obtained, theaddition of 0.2 percent, calculated as the solids content of UVAN 32varnish as the fluidizing agent proved to be markedly effective.

These compounds were kneaded together, and then polymerized in the samemanner as described in Example l. The flowability of the kneaded mixturewas sufficient, and it was easy to withdraw it from the ball mill. Thepolymer obtained was in the form of black, spherical particles having anaverage diameter of 15 microns. Olester-F7850X is a polyurethane typeresin having an SP of 10.0.

What is claimed is: I

1. In a process for producing a granular polymer by suspensionpolymerization, which comprises kneading a monomeric compositionconsisting essentially of a. at least one vinyl monomer, and

b. a vinyl monomer polymerization initiator, the improvement whichcomprises:

kneading into said monomeric composition, the following:

c. small particles of an inorganic compound, having a solubility inwater of not more than 10 percent, and

d. a resinous substance, acting as a fluidizing agent, having asolubility parameter value within the range of from 7.8 to 16.1 andbeing soluble in said monomeric composition, and

subsequently kneading said composition and then suspending the kneadedcomposition in an aqueous liquid medium to polymerize the vinyl monomer.

2. A process. according to claim 1 wherein said resinous substance is arelatively polar resin selected 8 300 percent by weight based on theweight of the vinyl monomer.

6. A process according to claim 2 wherein the polymer particle obtainedhas an average diameter of 15 microns or less.

7. A process according to claim 2 wherein saidresinous substance iscellulose ether resin.

8. A process according to claim 7 wherein said cellulose ether resin isethyl cellulose.

III l l l Q!

1. In a process for producing a granular polymer by suspensionpolymerization, which comprises kneading a monomeric compositionconsisting essentially of a. at least one vinyl monomer, and b. a vinylmonomer polymerization initiator, the improvement which comprises:kneading into said monomeric composition, the following: c. smallparticles of an inorganic compound, having a solubility in water of notmore than 10 percent, and d. a resinous substance, acting as afluidizing agent, having a solubility parameter value within the rangeof from 7.8 to 16.1 and being soluble in said monomeric composition, andsubsequently kneading said composition and then suspending the kneadedcomposition in an aqueous liquid medium to polymerize the vinyl monomer.2. A process according to claim 1 wherein said resinous substance is arelatively polar resin selected from the group consisting of celluloseether resins, polyurethane resins, amino resins, epoxy resins and alkydresins.
 3. A process according to claim 2 wherein said resinoussubstance is used in an amount of 0.001 to 10 percent by weight based onthe vinyl monomer.
 4. A process according to claim 3 wherein saidresinous substance is used in an amount of 0.001 to 1 percent by weightbased on the vinyl monomer.
 5. A process according to claim 2 whereinsaid inorganic compound is present in an amount of from 10 to 300percent by weight based on the weight of the vinyl monomer.
 6. A processaccording to claim 2 wherein the polymer particle obtained has anaverage diameter of 15 microns or less.
 7. A process according to claim2 wherein said resinous substance is cellulose ether resin.